1. Field of the Invention
The present invention relates to a particular plaintext detector.
2. Description of the Related Art
Currently, in order to avoid information leakage or manipulation in transmitting or storing information, information is received as plaintext to utilize an encryption algorithm for encrypting plaintext with a key, and the obtained ciphertext is transmitted or stored. In order to enhance the difficulty in decrypting such ciphertext, it is considered to be important that excellent encryption algorithms are used and that a user keeps a key secret, but plaintext subject to encryption is not traditionally considered to greatly affect the difficulty of decryption. In reality, attention is not given to it particularly. Moreover, it is troublesome to change to new encryption algorithms.
However, the inventor determines that ciphertext can be decrypted easily based on selected plaintext that is the plaintext satisfying certain conditions, depending on encryption algorithms.
Then, the difficulty of decryption can be enhanced without changing encryption algorithms by detecting the event that characteristic plaintext allowed for use in decryption has been inputted before encryption and taking proper schemes.